The invention relates to a vehicle headlamp comprising a light source which includes a plurality of opto-electronic elements.
The invention also relates to a vehicle provided with a headlamp.
Such headlamps are used on vehicles, such as cars, trucks, buses, bicycles and on vessels and aircraft.
Vehicle headlamps are known per se. A vehicle headlamp generally comprises an electric lamp with an incandescent body, for example, in a halogen-containing inert gas (a so-called halogen lamp), or an electric lamp with a pair of electrodes in an ionizable gas (a so-called discharge lamp). Such headlamps are customarily built up of two light sources which, in operation, generate either a so-called passing beam or a so-called main beam. Vehicle headlamps are known wherein the light source for the passing beam and the light source for the main beam are housed in a single lamp vessel (the so-called H4). Other known vehicle headlamps are those wherein two types of light sources are used, for example a halogen lamp in combination with a discharge lamp. There are also headlamps which, in operation, generate colored light, which is generally brought about by a suitable coating provided on an outer surface of the lamp vessel. U.S. Pat. No. 5,685,637 discloses a vehicle headlamp wherein a halogen lamp is combined with a ring of light-emitting diodes (LEDs).
The known vehicle headlamp has the drawback that, in principle, it constitutes a static lighting system.
It is an object of the invention to provide a vehicle headlamp of the type described in the opening paragraph, which exhibits more dynamic lighting possibilities.
To achieve this, the vehicle headlamp is characterized in accordance with the invention in that
a luminous flux of at least one of the opto-electronic elements amounts, in operation, to at least 5 lm,
and in that a light beam generated by the light source has a continuously adjustable spatial distribution.
Opto-electronic elements, also referred to as electro-optical elements, for example electroluminescent elements, such as light-emitting diodes (LEDs) with a luminous flux of 5 lm or more can suitably be used as a light source for vehicle headlamps. A relatively high luminous flux is necessary to ensure that also under ambient light conditions, for example sunlight or light originating from headlamps of other vehicles, sufficient light is generated so that a light beam generated by the light source can be observed sufficiently clearly from a distance.
To generate a so-called passing beam and/or a so-called main beam, a conventional vehicle headlamp requires a luminous flux ranging between 600 and 1000 lm to meet internationally standardized and specified light beam intensities. Current technology of opto-electronic elements, particularly that of light-emitting diodes, has yielded two different material systems which can suitably be used for different regions of the visible spectrum, i.e. A1-In-Ga-N for blue-green light and Al-In-Ga-P for yellow-red light. As a result, any desired spectral characteristic can be produced by combining suitable light-emitting diodes.
The use of a plurality of opto-electronic elements with a relatively high luminous flux enables a vehicle headlamp to be manufactured having much more dynamic lighting possibilities than the known vehicle headlamp. The opto-electronic elements can be switched on and switched off, with the spatial distribution of the generated light beam depending on the conditions. Said conditions may be influenced by conditions outside the vehicle, the so-called external conditions. External conditions include, for example, the general lighting level (day or night situation), the shape of the road (width, number of bends), the weather conditions (bright weather, fog, rain, snow, etc.) and the velocity at which and/or the direction in which the vehicle is moving. Conditions which also influence the spatial distribution may be determined by conditions inside the vehicle, the so-called internal conditions. Internal conditions include, for example, the shapes of the light beam as set or desired by the driver.
In the description of the current invention, a light beam having a continuously adjustable spatial distribution is to be taken to mean that the opto-electronic elements can be switched on and off in such a manner that the light beam can assume various shapes, which shapes may demonstrate a partial overlap and may, more or less gradually, merge. The luminous flux of the opto-electronic elements may be changed with respect to each other. If a light beam is adjustable, also the intensity and/or spectral characteristic of the light beam, or of segments of the light beam, may be different.
Since the spatial distribution is (continuously) adjustable, the driver""s view of the road and the surroundings of the vehicle is improved. On the one hand, objects situated on or in the axis of the light beam, such as oncoming traffic, can be better observed. On the other hand, also the observation of objects outside the center of the light beam is improved. This observation of objects outside the center of the light beam is also referred to as off-axis viewing, as opposed to the so-called on-axis viewing, which refers to the visibility of objects which are situated in the center, or in the immediate vicinity of the center, of the light beam. Examples of off-axis viewing include the observation of objects situated at or near the edge of the field of vision of the driver of the vehicle, for example the shoulder of the road, (unlit) objects, such as pedestrians or cyclists at the edge of the road on which the vehicle is traveling, and the observation of vehicles traveling on a road which crosses the road on which the vehicle provided with the headlamp in accordance with the invention is traveling.
The known vehicle headlamp has two light sources, namely a halogen lamp and a ring of light-emitting diodes, however, the halogen lamp produces a light beam of visible light and the LEDs emit infrared light at 880 nm. The individual light beams of the known vehicle headlamp are static in character and the light beam generated by the light source does not have a continuously adjustable spatial distribution.
An embodiment of the vehicle headlamp is characterized in accordance with the invention in that the light source consists of a plurality of opto-electronic elements. Consequently, the vehicle headlamp is composed of one type of light source. By combining LEDs or so-called multi-chip packages having a luminous flux in the range from 10-250 lm, the luminous flux of a suitable combination of 25 such elements, or fewer, preferably a combination of 15 such elements, or fewer, such as a combination of four such elements, meets the international standard ranging between 600 and 1000 lm. The dimensions of a vehicle headlamp comprising such a relatively small number of opto-electronic elements are comparable to the dimensions of a conventional vehicle headlamp. An additional advantage of the use of LEDs is that the service life of these opto-electronic elements is very long as compared to that of the conventional vehicle headlamp.
In a preferred embodiment of the vehicle headlamp in accordance with the invention, the spatial distribution of the light beam can be influenced by the velocity of the vehicle. In this manner, the range and the width of the light beam can be adjusted as a function of the velocity of the vehicle. At relatively low velocities, it is desirable for the light distribution of the light beam to be wider, so that, for example, also the shoulders of the road are illuminated. The higher the velocity of the vehicle, the longer the braking distance of the vehicle will be in general, so that it is desirable for the range of the light beam to increase. It may also be desirable for the width of the light beam to decrease and/or the intensity distribution between on-axis viewing and off-axis viewing to change. By switching on or off one or more opto-electronic elements at specific limiting values of the velocity of the vehicle, a continuously adjustable spatial distribution of the light emitted by the vehicle headlamp is obtained.
An embodiment of the vehicle headlamp is characterized in accordance with the invention in that the spatial distribution of the light beam can be influenced by the rotational position of a steering wheel of the vehicle. This enables the spatial distribution of the light beam of the vehicle headlamp to be adapted to the position of the steering wheel of the vehicle. The light beam xe2x80x9crotatesxe2x80x9d simultaneously, as it were, with the desired direction of movement of the vehicle. When the steering wheel is rotated it may be desirable for the intensity of the light beam shining in a straight line to decrease. By switching on or off one or more opto-electronic elements at specific limiting values of the rotational position of the steering wheel of the vehicle, a continuously adjustable spatial distribution of the light emitted by the vehicle headlamp is obtained.
In a favorable embodiment of the vehicle headlamp in accordance with the invention, the spatial distribution of the light beam can be influenced by the weather conditions. Under unfavorable weather conditions, in particular fog and snow, when the visibility is reduced by backscattering from fog or snow particles, the shape of the light beam can be adapted by activating different combinations of opto-electronic elements and by changing the output levels of the different opto-electronic elements. As a result of these adaptations, the overall spatial distribution of the light is changed.
An embodiment of the vehicle headlamp is characterized in accordance with the invention in that the spatial distribution of the light beam can be influenced by a driver of the vehicle. This enables the spatial distribution, for example the range and/or the width of the light beam, to be adjusted by the driver. As a result of information regarding, for example, the road type (for example a relatively narrow country road or a broad multi-lane motorway), the presence of bends and the possibility of oncoming traffic, it becomes desirable to make the light distribution driver-adjustable. On a country road, it is desirable to have a relatively broad light distribution of the light beam, so that also the shoulders of the road are clearly illuminated. On a motorway, where it is likely that there will be oncoming traffic, the degree to which the vehicle headlamp dazzles should not be too high, which is achieved in that the driver adjusts the light beam so as to be relatively narrow.
An alternative embodiment of the vehicle headlamp is characterized in accordance with the invention in that the spectral characteristic of a light beam generated by the light source depends upon the position in the light beam. By making the spectral characteristic of the light beam generated by the light source dependent on the position in the light beam, objects situated outside the center of the light beam can be better observed. Preferably, the light beam comprises at least two beam segments having a substantially different spectral characteristic. In general, the intensity of the light beam emitted by a vehicle headlamp decreases as a function of the position in the light beam, i.e. the intensity is maximal in the center of the light beam and gradually decreases in the direction of positions situated at a larger distance from the center of the light beam. As a result, the intensity of the light for so-called on-axis viewing is relatively much higher than for the so-called off-axis viewing.
It is well-known that the sensitivity of the human eye changes with the wavelength of the light and that equal quantities of energy of different wavelengths generally cause different sensations of brightness. In other words, if we consider a spectrum, and the received energy (per unit of time) is equal for all wavelengths, the middle of the visible region will apparently be brighter than the red and the blue ends. If the intensity of the light is relatively high (luminous efficiency xe2x89xa73.5 cd/m2), the maximum of the brightness lies at a wavelength of 555 nm (green/yellow), the so-called photopic eye-sensitivity curve. At this wavelength, particularly the cones are active in the human eye. If the intensity of the light is relatively low (luminous efficiency xe2x89xa60.035 cd/m2), the maximum of the brightness lies at a wavelength of 507 nm (blue/green or cyanblue), the so-called scotopic eye-sensitivity curve. At this wavelength, particularly the rods are active in the human eye.
It is advantageous to bring about substantially different spectral characteristics of the light beam for the on-axis and the off-axis parts of the light beam. In particular, in the off-axis parts of the light beam, the spectral characteristic of the light is adapted to a light intensity which is relatively low. By thus making the spectral characteristic of the light beam generated by the light source dependent upon the position in the light beam, the visibility of objects situated outside the center of the light beam is improved.
It is noted that, in practice, also photopic and scotopic light beams preferably have a broad spectrum, which light beams both have a more or less xe2x80x9cwhitexe2x80x9d appearance. The difference between a photopic and a scotopic light beam corresponds, as it were, to a difference between a light beam having a high and a low color temperature.
There is a possibility that the above-mentioned beam segments may comprise segments demonstrating a partial overlap. A possibly non-continuous transition between the beam segments may be perceived as unpleasant by the driver of the vehicle.
Preferably, a first beam segment has a spectral characteristic which is rich in green-yellow light, and a second beam segment has a spectral characteristic which is rich in blue-green light. On the one hand, in the on-axis part of the light beam (the first beam segment) a spectral characteristic of the light is presented which is adapted to the photopic eye-sensitivity curve, i.e. rich in green-yellow light. On the other hand, in the off-axis parts of the light beam (the second beam segment) a spectral characteristic of the light is presented which is adapted to the scotopic eye-sensitivity curve, i.e. rich in blue-green light.
These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.